The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
This invention relates to advanced high-speed marine vehicles. More particularly, this invention is to a hybrid SES/hovercraft having a retractable skirt system.
Two primary types of high-speed advanced marine vehicles are the surface effect ship (SES) (or surface effect vehicle (SEV)) and the fully skirted hovercraft. Both are considered air-cushioned vehicles (ACV) in that each rides on a pressurized cushion of air. The air cushion serves to separate the vehicle from the surface over which it operates, allowing freer movement while greatly decreasing the hydrodynamic drag. The lower drag allows much greater speeds to be achieved at lower drive power when compared to conventional displacement hulls. In each case powered lift fans are needed to maintain the flow of volumes of pressurized air under the vehicle due to the flow of air escaping from the cushion.
The air cushion of the hovercraft is contained around its perimeter by a flexible bag and finger skirt system which conforms to the irregular operating surface be it waves or uneven terrain, thereby greatly reducing the flow of air escaping from the cushion. The air cushion of the SES or SEV is contained on the sides by relatively thin, rigid, lateral walls contacting and protruding into the water, and at the front and rear by flexible or semi-flexible seals or skirts. Though the hovercraft skirt theoretically can have a lower drag due to the air gap which would give no interaction with the surface, in reality considerable drag can be experienced in rougher water due to wave interaction with the skirt""s fingers. So, the SES will have considerably lower hydrodynamic drag in rougher water due to the thinness and rigidity of the side-walls as opposed to the unwieldy side portion of the skirt of the hovercraft. A further advantage of the SES is that since its side-walls protrude below the water surface there is practically no air loss out the sides. The reduced drag of the SES reduces the thrust required to achieve a given speed, and the reduced air loss reduces the power required for the lift fans. In addition, water-jet or other water propulsion means may be employed with the SES which are generally more efficient than air-propellers on hovercraft. Also, the operational costs of the side-walls on the SES are much lower when compared to the side portions of the skirt of the hovercraft. This is because the side portions of the skirt of the hovercraft are composed of a multitude of components made of flexible materials which are prone to wear and damage and, due to waves, are in constant contact with the water surface while underway. However, despite the advantages of the SES, its rigid side-walls mean that it is strictly a non-amphibious vehicle, and is limited to water-borne operations of suitable depth. In contrast to the SES, the hovercraft is a truly amphibious vehicle with is capable of traversing on dry land as well as open water, and it can also operate effectively on soft mud, marsh, or tidal flats that are impassible to any other vehicle.
Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for a watercraft that can operate as a high speed SES in open water and can deploy a retracted skirt to operate as a hovercraft across beaches and overland.
An object of the invention is to provide a hybrid SES/hovercraft having a retractable skirt.
Another object of the invention is to provide a hybrid SES/hovercraft having lateral rigid thin walls of an SES for high-speed travel across open water and a flexible skirt of a hovercraft for transitioning beaches and overland.
Another object of the invention is to provide a hybrid craft to operate as an SES when in suitably deep water and with the skirt retracted yet will still be capable of full amphibious operations in a hovercraft mode with the skirt deployed.
Another object of the invention is to provide a hybrid craft having a retractable skirt to reduce wear and tear on the skirt that may occur during high-speed transit in open water.
Another object of the invention is to provide an amphibious hybrid craft having a retractable skirt and rigid thin side-walls to reduce air losses and drag and to permit greater speed during high-speed transit in open water.
These and other objects of the invention will become more readily apparent from the ensuing specification when taken in conjunction with the appended claims.
Accordingly, the present invention is to be a hybrid craft. The hybrid craft has a hull having a downwardly extending boundary structure on the periphery of the hull to reach through the surface of water. The boundary structure has thin rigid side-walls extending downward from lateral sides of the hull, a forward seal wall extending downward from a forward portion of the hull, and an aft seal wall extending downward from an aft portion of the hull. Means mounted on the hull creates a pressurized cushion of air under the hull inside of the boundary structure to support and transport the hull on the water on an air cushion. A flexible skirt system is mounted on the hull inwardly of and adjacent to the boundary structure to retract to a first position above the boundary structure the surface of the water and to extend to a second position below the boundary structure and the surface of the water to allow transit across beaches and overland.